1. Field of the Invention
This invention relates generally to optical elements, such as corrective lenses, and to methods for making them. More particularly, this invention relates to optical elements containing two or more polymers.
2. Description of the Related Art
Many optical systems such as the human eye contain aberrations. In attempting to correct for such aberrations, it is common to assume that the light passing through the system is limited to paraxial rays, specifically, rays that are near the optical axis and that are contained within small angles. Corrective optics produced according to this assumption generally have only spherical surfaces. For example, it is typically assumed that ocular imperfections in the human eye are limited to lower order imperfections, including the imperfections commonly called “astigmatism” and “defocus”, that can be corrected by lenses having spherical surfaces. However, higher order imperfections can exist, including but not limited to imperfections known as “coma” and “trefoil.” These imperfections unfortunately cannot be corrected by conventional glasses or contact lenses, leaving patients with less than optimum vision even after the best available corrective lenses have been prescribed.
Moreover, it is often difficult to simultaneously minimize all aberrations. Indeed, corrections to an optical system to minimize one type of aberration may result in the increase in one of the other aberrations. For example, decreasing coma can result in increasing spherical aberrations. Furthermore, it is often necessary to correct aberrations in an optical system that are introduced during manufacturing. This process can be iterative and time consuming, requiring, as it does, assembly, alignment, and performance evaluation to identify aberrations, followed by disassembly, polishing or grinding to correct the aberrations, and then reassembling and retest. Several iterations might be needed before a suitable system is developed.
U.S. patent application Ser. No. 09/875,447, filed Jun. 4, 2001, entitled “Wavefront Aberrator and Method of Manufacturing,” discloses, inter alia, a method for making a wavefront aberrator by using a photopolymerization method to change the refractive index of a polymer. A refractive index profile may be formed by selectively curing the polymer on a region-by-region basis by exposure to radiation (e.g., UV light). The refractive index of the exposed polymer in the selected regions increases, but the resulting refractive index profile is not permanent, and over time, the refractive index profile changes and the amplitude of the induced refractive index change tends to decrease over time.